airborne technologies for disaster management · 2019-08-28 · airborne technologies for disaster...

AIRBORNE TECHNOLOGIES FOR DISASTER MANAGEMENT

Jürgen Schulz

Hansa Luftbild AG, 48147 Münster, Germany, [email protected]

KEY WORDS: airborne remote sensing, flooding, urban flash floods, bark beetle

ABSTRACT:

Currently, satellite-based systems and UAVs are very popular in the investigation of natural disasters. Both systems have

their justification and advantages - but one should not forget the airborne remote sensing technology. The presentation shows

with three examples very clearly how airborne remote sensing is still making great progress and in many cases represents the

optimal method of data acquisition.

The airborne detection of forest damages (especially currently the bark beetle in spruce stands) can determine the pest attack

using CIR aerial images in combination with ALS and hyperspectral systems - down to the individual tree. Large forest areas

of 100 sqkm and more can be recorded from planes on one day (100 sqkm with 10cm GSD on one day).

Flood events - such as on the Elbe in 2013 - were recorded by many satellites. However, many evaluations require high-

resolution data (GSD 10cm), e.g. to clarify insurance claims. Here the aircraft system, which was able to fly below the cloud

cover and was constantly flying at the height level of the flood peak, proved to be unbeatable.

The phenomenon of urban flash floods is one of the consequences of climate change. Cities are not in a position to cope with

the water masses of extreme rain events and so are confronted with major damages. In Germany, a number of cities are

already preparing to manage short-term but extreme water masses. The complicated hydrographic and hydraulic calculations

and simulations require above all one thing - a precise data basis. This involves, for example, the height of kerbstones and the

recording of every gully and every obstacle. Such city-wide data can only be collected effectively by photogrammetric

analysis of aerial photography (GSD 5 to 10cm).

1. INTRODUCTION

Airborne remote sensing has a long tradition in which

Hansa Luftbild played a decisive role. Founded in 1923,

Hansa Luftbild quickly became the largest aerial

photography company in the world, flying through

Antarctica, Greenland, Afghanistan, China and Peru. A

mountain range in the Antarctic is still named after the

pilot of Hansa Luftbild "Bundermann Chain".

Fig 1: Hansa Luftbild Photograph Fig 2: Bundermann Chain (Antarktis)

Max Bundermann

Today, Hansa Luftbild is a leading European company in

the fields of airborne remote sensing, photogrammetry,

laser scanning and geodata processing - however, due to

technical developments and the competitive situation, this

position has to be constantly redefined.

According to an increasing number of technical articles,

airborne remote sensing will soon be replaced by satellite

data and drones. In fact, there is enormous technical

progress in satellites and drones, so such an assessment

seems realistic. But is the importance of airborne geodata

acquisition really diminishing - or is it even becoming

superfluous?

A brief comparison of the systems with regard to the

topic of "disaster management" gives a differentiated

picture.

The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLII-3/W8, 2019 Gi4DM 2019 – GeoInformation for Disaster Management, 3–6 September 2019, Prague, Czech Republic

This contribution has been peer-reviewed. https://doi.org/10.5194/isprs-archives-XLII-3-W8-387-2019 | © Authors 2019. CC BY 4.0 License.

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Satellite data have a big advantage - the satellite orbits

the earth and can capture virtually any location (or

disaster). If it is a satellite family, disasters can be

identified very shortly after their occurrence and

measures to save human lives can be supported at short

notice. There are already many examples of this,

including earthquake disasters and floods. On the other

hand, there are serious disadvantages - you fly above the

cloud cover, which optical sensors cannot penetrate.

Another disadvantage is the geometric resolution. A high

resolution (currently 30cm) is very expensive due to the

commercialization of satellite remote sensing. With its

Copernicus program, the European Union offers an

important alternative - the data are free of charge, but

currently with resolutions of 10 meters at Sentinel-2.

Relatively low flying drones seem to be the solution to

capture the extent of a disaster with high detailing. The

current development of the drones and their sensors is

breathtaking. Optical sensors, laser scanners and

hyperspectral technology mounted on drones allow the

highest resolutions and accuracies. There are now so

many providers of the most diverse technical designs of

drones that geo-exhibitions (such as Intergeo in

Germany) effortlessly fill a large hall exclusively with

drones.

However, there are clear limits to the use of drones in

disaster situations. On the one hand, the systems in

question are classified as “aircraft” and are thus subject to

the requirements of the authorities for flight safety as

well as aircraft (application for a permit to fly, etc.).

Furthermore, there are national regulations for the

operation of drones. In Germany, for example, it is not

permitted to operate drones outside the field of vision of

the drone pilot. This significantly limits the coverage of

larger areas. In any case, there are clear limits to the use

of drones in large disaster areas (e.g. floods); the high

time and personnel requirements also lead to high costs.

Satellite data and the use of drones therefore have many

advantages for the collection of geodata in the event of a

disaster - but also very clear disadvantages. Ultimately,

the type, location and extent of the disaster will determine

which data is required. This dialectic of advantages and

disadvantages naturally also applies to the airborne

acquisition of geodata. However, there are a strikingly

large number of applications where the most valuable

information for coping with disasters is provided by

aircraft. From flight altitudes between approx. 200-800

meters the necessary information can be obtained

quickly, comprehensively and up-to-date with a good

accuracy. This compensates for some disadvantages, such

as the relatively high costs. And, unfortunately, cross-

border operations are still very difficult due to the

different legislation and the associated difficulties in

obtaining a permit to fly in a neighbouring country.

Three very different examples will be used in the

following to demonstrate how airborne remote sensing

can achieve optimum results in disaster situations.

2. FLOODS AT RIVERS

In 2013 there was an extreme flood event on one of the

largest German rivers - the Elbe. Caused by heavy

rainfall in the Czech Republic followed by flooding in the

Czech Republic, the peak of the flood reached Germany

at the beginning of June and moved to Hamburg within a

few days only. Large areas along the Elbe, Saale and

Mulde rivers were flooded. An impression is given by

figure 3.

Fig 3: Flooding of river Elbe (taken from Hansa Luftbild airplane)

Hansa Luftbild received the demanding order to record

this damage event by means of aerial photographs.

The decisive challenge was to capture the pictures with a

geometric resolution of 10 cm. At the same time, the

images should always be taken at the peak of the tidal

wave. This set a very narrow time window, i.e. in view of

the – of course - bad weather it was necessary to fly

below the cloud cover.



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The task could be solved by using a camera DMC-1

(Zeiss/Intergraph; now Hexagon) mounted on a twin-

engine Cessna-404. In order to achieve a GSD of 10cm

with this camera, a flight altitude of 1000 meters above

ground must be maintained - so that one could mostly

stay under the clouds.

The flood area was huge and stretched from the German-

Czech border South of Dresden to shortly before

Hamburg, supplemented by the floods of the tributaries

Saale and Mulde. The total length was 983 river

kilometres and the area 2,471 square kilometres. 16,693

coloured aerial photos were taken.

date photos region

05.06.2013 2.952 River Mulde

06.06.2013 1.510 River Saale North

07.06.2013 3.086 River Saale South

07.06.2013 1.922 River Elbe South

08.06.2013 591 River Elbe South

09.06.2013 2.992 Elbe and Rosenburg

10.06.2013 1.087 Elbe to Wittenberge

11.06.2013 1.988 Elbe and Fischbeck

12.06.2013 5.65 River Elbe North

16.693

Table 1: Project timeline

The flood areas were so large that many parallel flight

strips were necessary.

Fig 4: Flight planning near Magdeburg (excerpt)

Fig 5: Project area Elbe, Saale and Mulde

The situation was aggravated by two severe dam breaches

(Rosenburg and Fischbeck) during the project. Here the

flight planning had to be changed very quickly so that the

new areas could be recorded at short notice.

Of course the flood was also observed by various

satellites, but optical data with 10cm resolution below the

cloud cover could not be obtained. And for a drone

mission the area was simply much too large.

Image data could thus be obtained under very difficult

conditions - but the decisive factor is how this

information was used for disaster management. For

example, Hansa Luftbild was able to participate in

follow-up projects in which the aerial photographs were

used to precisely define the water-land boundary. In this

way, the aerial photographs served to settle claims for

damages by insurance companies.

But far more important are the hints for the planning of

new protective measures (raising the dike by identifying

weak points in the dike system, designating polder areas,

renaturing water bodies, improving the safety of fuel oil

tanks, etc.).

The evaluation of the data also served to improve cross-

border flood risk management (in this case in particular

the cooperation of German and Czech authorities).

3. URBAN FLASH FLOODS

The second example of airborne disaster management

also has something to do with "too much water", but it

does not announce itself several days before as in the first

example. In the case of so-called urban flash floods (or

heavy rainfall events), water comes out of the clouds in

extreme quantities without prior notice. Climate change

means that we increasingly have short, extreme weather

events - including flash floods of this kind. Cellars and

underground garages that are full to capacity with rain



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water are very annoying, but in some cases there is also

danger to life and limb.

It is impossible to record such events by satellite, airplane

or drone, because the event often lasts only a few hours

or less. The damage, on the other hand, is enormous,

especially of course if the area is inhabited. Subsequent

damage mapping is of course feasible with remote

sensing. The better way, however, is to provide the

appropriate geoinformation for damage prevention or at

least damage limitation. This enables local authorities to

prepare for such events.

In Germany there are already the first municipalities that

use geodata for protection against urban flash floods. Not

only because they are legally obliged to take precautions,

but also because many municipalities have already had

negative experiences. This includes Münster, Hansa

Luftbild's home town (see Figure 6).

Fig 6: Urban Flash Flood in Münster city Fig 7: Urban Flash Flood,

(Source: dpa/cas fdt) Water in a private house

The key questions with this problem are "Where does the

water flow to?" and "Where does it damage?". This

requires a local, detailed model-based investigation. Such

a simulation requires good input data. Some of these data

should be available in every municipality (building stock,

sewer data, etc.). Other data are not available or of

insufficient quality (elevation model, break lines, etc.).

Figure 8 shows a section of a medium-sized city on the

edge of the Black Forest, which was flown by Hansa

Luftbild in spring 2019 (GSD 5cm, overlaps 60%/50%).



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Fig 8: Basic image for a risk map

A digital elevation model (DEM) was generated by a

matching process of the aerial photographs. One can

clearly see that the terrain in the upper part of the image

(North) is higher, so the water will mainly flow from

North to South. However, break lines were also

measured. These show that the water is dammed at the

upper light green east-west road and forced in certain

directions. South of this road there are dark green areas

which represent depressions and thus collect the water.

The residential buildings located there are very

susceptible to flooding. If there is also a kindergarten

underneath, the situation may become dramatic.

It is therefore necessary to provide precise data on the

possible flow paths of the water (i.e. also the height of the

kerbs, the location of each gully, and the detection of

each obstacle).

In addition to the data on the urban sewerage system, this

is all important input information for a hydraulic

simulation. There are numerous commercial programs for

this and there are specialized companies with which

Hansa Luftbild cooperates.

Finally, it is about the production of hazard maps or risk

maps of an urban area, which provide vital information

for urban planning, urban drainage, disaster control and

the public. The data can be used to prevent heavy rainfall,

e.g. by

- construction of drainage ditches and rainwater retention

basins

- unsealing of surfaces or replacement by water-

permeable surface coverings

- erection of obstacles (walls) to force flowing water in

directions

- roof greenings

- keeping areas free for natural infiltration, creating green

areas

Danger of urban flash floods is real and one has to

prepare the protection from them seriously. Good

simulation programs also require good geodata as a basis.

Airborne remote sensing - and apparently only this - can

provide the required accurate geodata.

4. FOREST DAMAGE CAUSED BY BARK

BEETLES

Drought and pest infestation have dramatically worsened

the condition of our forests in recent years. In addition,

there were storms such as the recent storm "Eberhard".

There is no doubt that global climate change is also

increasingly causing extreme weather events that damage

forests, to which forest administrations and forest owners

must respond.

Above all, special attention must urgently be paid to the

rampant bark beetle infestation in order to prevent or at

least limit its further spread. This requires an up-to-date

knowledge of the affected areas, ideally early detection.

The known forest methods (visual terrestrial observation

by forest specialists, pheromone traps, etc.) are currently

reaching their limits and should be supplemented by

detailed information from the air.

The basic advantages of remote sensing become clearly

visible - namely to provide data up-to-date, fast and

homogenously area-wide.

Airborne remote sensing can primarily offer visible and

near infrared airborne surveys. For special applications

the "Airborne Laser Scanning" and the hyperspectral

flights or a combination of these data is useful.

In the summer of 2018 Hansa Luftbild was asked to carry

out a project for the State enterprise “Sachsenforst”, in

which the National Park "Saxon Switzerland" at the

German-Czech border was captured using aerial photos

(10 cm pixels) and digital orthophotos were produced.

The purpose of this inventory was to identify forest areas

damaged by the bark beetle.



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Fig 9: Ortho photo National Park „Sächsische Schweiz", obtained and processed by Hansa Luftbild

(reddish: healthy stands; grey: infested stands)

As the photo shows, such areas can be well delimited by

means of visual control. Of course, typical signs of

infestation, such as drilling dust at the base of the trunk,

are not visible in aerial photographs - but crown

discoloration and crown thinning indicate the activity of

the bark beetle and are clearly visible in the aerial

photograph. Particularly in the infrared range (as in the

picture above) the damage picture and - with repeated

flights - the damage process can be represented well and

thus also an early detection is possible. The intersection

of these data with existing information in a GIS (forest

operation maps, forest type maps, ...) supports semi-

automatic screening and infestation detection.

Of course, special flights are correspondingly complex.

On the other hand, 100 sqkm of forest with 10cm pixels

can be captured on a single (cloud-free) day; in the colour

and infrared range with the possibility of single tree

assessment.

For a good damage mapping, image data with at least

20cm resolution are necessary, which again places the

airborne remote sensing in the foreground.

However, the big challenge with the problem "bark

beetle" is its early detection.

In general, the physiological needle changes during pest

infestation are divided into three phases: green, red and

grey. Damage in the red phase (visible discoloration of

the needles) and in the grey phase (few/no needles and

grey trunk) can already be sufficiently detected in the

aerial photograph (see above). The focus is on the

identification of dead trees and the area-related

documentation of damage. However, it is very desirable

to enable early detection of bark beetles already in the

green phase and thus to allow early human intervention.

The transition from the green to the red phase has a very

complex background; there is, however, a well-founded

assumption that disturbances in the pigment balance are

causal and are reflected spectrally. Narrow-band

wavelengths (e.g. at 717 nm) could support a distinction

between "infested" and "uninfected" at an early stage of

beetle infestation.

Airborne hyperspectral sensors offer the possibility to

detect in such specific wavelengths, but the detection of

forest areas is not yet very common. Hansa Luftbild is

cooperating with the Hungarian company Envirosense.

Initial results give reason to hope that hyper spectroscopy

will be used to detect early bark beetle damage.



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Fig 10: Differentiation of tree types by means of hyper spectroscopy

Figure 10 shows the result of a combined hyperspectral

and laser data evaluation. The images were taken with an

AISA Kestrel10 hyperspectral sensor (1.0m ground pixel)

and a Leica ALS70 laser system (8 points/sqm). The use

of pixel-based and object-based classification programs

allowed the production of a tree species map.

This method is currently being further developed in the

direction of early detection of forest damage. The

hyperspectral method will certainly receive a boost with

the launch of the Copernicus satellite EnMAP next year.

5. SUMMARY

Three selected examples showed that airborne

technologies make valuable and unique contributions to

disaster management.

Despite enormous progress in satellite and drone

technology, this will obviously remain the case for many

years to come.

ACKNOWLEDGEMENTS

The author wishes to thank the State enterprise

Sachsenforst for the permission to use figure 9. The

author also wishes to thank company Envirosense Kft.

(Hungary) for the good cooperation and for the

permission to use figure 10.



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airborne technologies for disaster management · 2019-08-28 · airborne technologies for disaster...

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